Meiosis
Make a cover page:
•Your Name
•Chapter 11
•Meiosis
Feel free to decorate
your cards as you
go!
(2 separate flashcards)
• Diploid
– 2 sets of chromosomes in
a cell.
– ½ from mom, ½ from dad.
– 2n
– All body cells are diploid.
– Made by MITOSIS.
• Haploid
– 1 set of chromosomes
in a cell.
– 1n
– All sex cells are
haploid.
– Made by MEIOSIS.
Not a flashcard.
DIPLOID vs. HAPLOID
1n
egg
Haploid
+
+
+
1n
sperm
Haploid
=
=
=
2n
new organism
DIPLOID
Gametes
• Another name for sex cells: egg & sperm
Zygote
• A fertilized cell.
• 2 gametes that are now together.
Not a flashcard.
In case you’ve never seen it for
real…this is human DNA.
Not a flashcard.
This is a DIPLOID cell’s DNA. (2n)
23 Homologous pairs – one from mom and one from dad
To do this,
MITOSIS
is used.
Not a flashcard.
This is a HAPLOID cell’s DNA. (1n)
To do this,
MEIOSIS
is used.
Meiosis
• The making of gametes (eggs & sperm).
• Cells contain ½ the normal amount of
chromosomes. (haploid)
Meiosis
Why is meiosis necessary?
• If the sex cells didn’t have ½ the amount of
chromosomes, what would happen when the
sperm & egg made a zygote?
• Answer: Each baby would have twice the
number of chromosomes as the parents!!!
egg
zygote
sperm
26
+
26
=
52!
WOW!
That’s 2
full sets!
What is produced in meiosis?
• 4 haploid cells (1n)
• Each cell is genetically different! Cool!
Not a flashcard.
The cells produced during meiosis have
DIFFERENT DNA!
Not a flashcard.
Review Meiosis Facts
4 cells genetically
• Makes ____
different from parent cell & from
each other
1n cells (1n or 2n?)
• Makes _____
Gametes (sperm & eggs)
• Makes ________________
sexual reproduction
• Used for ______________
Spermatogenesis
• Makes 4 sperm cells.
Oogenesis
• Makes 1 egg. (and 3 polar bodies)
Not a flashcard.
Spermatogenesis vs. Oogenesis
Not a flashcard.
What is different about meiosis?
• Many different variations in the
gametes.
Makes
cells with different genes than parent cell
___________________________________
• Divides twice, but only copies DNA
once.
Makes
cells with ½ the number of chromosomes as parent cell
___________________________________
Phases of Meiosis
I PMAT PMAT
Meiosis 1
Meiosis 2
(I Peed on the MAT twice!) 
Meiosis
Meiosis
I
P
P
M
A
T
cytokinesis
M
A
T
cytokinesis
Mitosis vs Meiosis
Interphase Interphase I
• DNA spread out as chromatin
• Nuclear membrane visible
• DNA copied during S phase
Same as mitosis!
Mitosis vs Meiosis
Prophase Prophase I
• DNA scrunches into
Same, except…
chromosomes
Homologous pairs match up
• Nuclear membrane disappears
XX
X
• Centrioles appear
XX
X
X
XX
Crossing Over
• Chromatid arms trade
DNA with each other.
• Produces daughter cells
with different gene
combinations.
Mitosis vs Meiosis
Metaphase Metaphase I
• Chromosomes line up
in middle
Chromosomes line up
in middle with
homologous partner
Mitosis vs Meiosis
Anaphase Anaphase I
• Chromatids split •Chromatids stay together
and move apart. •Homologous pairs move
apart
Mitosis vs Meiosis
Telophase Telophase I
• Two nuclei
Same as mitosis!
• Nuclear membrane returns
• DNA spreads out as
chromatin
Mitosis vs Meiosis
Cytokinesis Cytokinesis I
• Cytoplasm splits
into 2 cells
Same as mitosis!
Mitosis vs Meiosis
Prophase Prophase II
• DNA scrunches into
chromosomes
• Nuclear membrane
disappears
• Centrioles appear
Same as mitosis!
Mitosis vs Meiosis
Metaphase Metaphase II
• Chromosomes line up
in middle
Same as mitosis!
Mitosis vs Meiosis
Anaphase Anaphase II
• Chromatids split
and move apart
Same as mitosis!
Mitosis vs Meiosis
Telophase Telophase II
• Two nuclei
• Nuclear membrane
returns
• DNA spreads out as
chromatin
Same as mitosis!
Mitosis vs Meiosis
Cytokinesis Cytokinesis II
• Cytoplasm splits
Same as mitosis!
Mitosis vs Meiosis
In Meiosis:
• (Prophase I) Homologous pairs match up.
• (Prophase I) Crossing over creates
genetic differences.
• Cells divide twice but only copies DNA
once- this makes haploid cells.
Meiosis
The end. Really.
• Test date:
• How to succeed on GHS biology tests:
– Memorize the flashcards.
• Practice with friends, by yourself, or with family.
– Read the book.
• It is easy reading.
• Reading the text helps you understand the written part.
– Do all labs, homework, and worksheets.
• If you missed any days, make sure you made up any work!